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United States Patent |
5,741,998
|
Hinshaw
,   et al.
|
April 21, 1998
|
Propellant formulations based on dinitramide salts and energetic binders
Abstract
Composite propellant formulations are disclosed having a dinitramide salt
oxidizer, such as ammonium dinitramide, an energetic binder, such as
energetically substituted oxetane and oxirane polymers, a reactive metal,
such as aluminum, and other typical propellant ingredients such as
curatives and stabilizers. Propellant formulations useful for minimum
smoke or reduced smoke applications, preferably include little or no
reactive metal. The disclosed propellant formulations are able to combust
the reactive metal efficiently, possess high burn rates, and produce
little or no HCl exhaust gases.
Inventors:
|
Hinshaw; Carol J. (Ogden, UT);
Wardle; Robert B. (Logan, UT);
Highsmith; Tom K. (North Ogden, UT)
|
Assignee:
|
Thiokol Corporation (Ogden, UT)
|
Appl. No.:
|
614303 |
Filed:
|
March 12, 1996 |
Current U.S. Class: |
149/19.6; 149/19.4 |
Intern'l Class: |
C06B 045/10 |
Field of Search: |
179/19.4,19.6
|
References Cited
U.S. Patent Documents
3609115 | Sep., 1971 | Herring.
| |
3645809 | Feb., 1972 | Stow, Jr.
| |
3680483 | Aug., 1972 | Staudacher et al.
| |
3687954 | Aug., 1972 | Tyler, III et al.
| |
3811358 | May., 1974 | Morse.
| |
3953258 | Apr., 1976 | Sayles.
| |
4158583 | Jun., 1979 | Anderson.
| |
4410376 | Oct., 1983 | Bruenner et al.
| |
4707540 | Nov., 1987 | Manser et al.
| |
4804424 | Feb., 1989 | Hinshaw.
| |
4915755 | Apr., 1990 | Kim.
| |
5076868 | Dec., 1991 | Doll et al.
| |
5120827 | Jun., 1992 | Willer et al.
| |
5198204 | Mar., 1993 | Bottaro et al.
| |
5271778 | Dec., 1993 | Bradford et al.
| |
5324075 | Jun., 1994 | Sampson | 149/19.
|
5529649 | Jun., 1996 | Lund et al. | 149/19.
|
5587553 | Dec., 1996 | Braithwaite | 149/19.
|
Primary Examiner: Miller; Edward A.
Attorney, Agent or Firm: Cushman Darby & Cushman IP Group of Pillsbury
Madison & Sutro, LLP
Parent Case Text
RELATED APPLICATION
This application is a continuation-in-part of application Ser. No.
08/052,035, now U.S. Pat. No. 5,498,303 filed Apr. 21, 1993 and entitled
"PROPELLANT FORMULATIONS BASED ON DINITRAMIDE SALTS AND ENERGETIC
BINDERS," which application is incorporated herein by this reference.
Claims
What is claimed is:
1. A composite propellant formulation comprising:
an energetic binder in the range from about 10% to about 35% by weight of
the composite propellant formulation, wherein the energetic binder is
selected from energetically substituted oxetane polymers having a formula:
##STR6##
where X is --NO.sub.2, --ONO.sub.2, --N.sub.3, --NF.sub.2, or --H and Y is
--NO.sub.2, --ONO.sub.2, --N.sub.3, or --NF.sub.2, energetically
substituted oxirane polymers having a formula:
##STR7##
where X is --NO.sub.2 or --N.sub.3, and energetic nitramine polyester
polymers based on nitraminodiacetic acid and a diol or mixture of diols,
wherein said diol is an aliphatic diol containing from 2-6 carbon atoms
and primary alcohol functional groups;
a solids loading of from about 65 to 90% by weight of the composite
propellant formulation, wherein said solids loading comprises:
a dinitramide salt oxidizer; and
a reactive metal; and
a polyfunctional curative.
2. A composite propellant formulation as defined an claim 1, wherein the
dinitramide salt oxidizer is ammonium dinitramide (ADN).
3. A composite propellant formulation as defined in claim 1, wherein the
dinitramide salt oxidizer is tetrazolium dinitramide.
4. A composite propellant formulation as defined in claim 1, wherein the
dinitramide salt oxidizer is ammonium-tetrazole dinitramide.
5. A composite propellant formulation as defined in claim 1, wherein the
dinitramide salt oxidizer is aminoammoniumfurazan dinitramide.
6. A composite propellant formulation as defined in claim 1, wherein the
energetic binder is poly(glycidyl nitrate).
7. A composite propellant formulation as defined in claim 1, wherein the
energetic binder is poly(glycidyl azide).
8. A composite propellant formulation as defined in claim 1, wherein the
energetic binder is an energetically substituted oxetane polymer selected
from poly-NMMO (poly(nitratomethyl-methyloxetane)), poly-BAMO
(poly(bisazido-methyloxetane)), poly-AMMO
(poly(azidomethyl-methyloxetane)), poly-NAMMO
(poly(nitraminomethyl-methyloxetane)), copoly-BAMO/NMMO, copoly-BAMO/AMMO,
and mixtures thereof.
9. A composite propellant formulation as defined in claim 1, wherein the
energetic binder is 9DT-NIDA
(diethylene-glycoltriethyleneglycolnitraminodiacetic acid terpolymer).
10. A composite propellant formulation as defined in claim 1, wherein the
reactive metal has a concentration greater than 5% by weight.
11. A composite propellant formulation as defined in claim 1, wherein the
reactive metal is aluminum.
12. A composite propellant formulation as defined in claim 1, wherein the
reactive metal is magnesium.
13. A composite propellant formulation as defined in claim 1, wherein the
reactive metal is an aluminum-magnesium alloy.
14. A composite propellant formulation as defined in claim 1, wherein the
reactive metal is boron.
15. A composite propellant formulation as defined in claim 1, further
comprising from about 0% to about 15% by weight ammonium perchlorate,
wherein the combined amount of the ammonium perchlorate and the
dinitramide salt oxidizer in the composite propellant formulation does not
exceed about 70% by weight.
16. A composite propellant formulation as defined in claim 1, further
comprising from about 0% to about 20% by weight ammonium nitrate, wherein
the combined amount of ammonium nitrate and the dinitramide salt oxidizer
in the composite propellant formulation does not exceed about 70% by
weight.
17. A composite propellant formulation comprising:
an energetically substituted oxetane polymer binder in the range from about
10% to about 35% by weight of the composite propellant formulation,
wherein the energetically substituted oxetane polymer has a formula:
##STR8##
where X is --NO.sub.2, --ONO.sub.2, --N.sub.3, --NF.sub.2, or --H and Y is
--NO.sub.2, --ONO.sub.2,--N.sub.3,or --NF.sub.2 ;
a solids loading of from about 65 to 90% by weight of the composite
propellant formulation, wherein said solids loading comprises:
a dinitramide salt oxidizer selected from ammonium dinitramide (ADN),
tetrazolium dinitramide, armmoniumtetrazole dinitramide,
aminoammoniumfurazan dinitramide, and mixtures thereof; and
a reactive metal selected from aluminum, magnesium, aluminum-magnesium
alloys, boron, and mixtures thereof; and
a polyfunctional curative.
18. A composite propellant formulation comprising:
an energetically substituted oxirane polymer binder in the range from about
10% to about 35% by weight of the composite propellant formulation,
wherein the energetically substituted oxirane polymer has a formula:
##STR9##
where X is --NO.sub.2 or --N.sub.3 ; a dinitramide salt oxidizer in the
range from about 50% to about 70% by weight of the composite propellant
formulation, wherein the dinitramide salt oxidizer is selected from
ammonium dinitramide (ADN), tetrazolium dinitramide, ammoniumtetrazole
dinitramide, aminoammoniumfurazan dinitramide, and mixtures thereof;
a reactive metal in the range from about 0% to about 25% by weight of the
composite propellant formulation, wherein the reactive metal is selected
from aluminum, magnesium, aluminum-magnesium alloys, boron, and mixtures
thereof; and
a polyfunctional curative.
19. A composite propellant formulation comprising:
an energetic nitramine polyester polymer based on nitraminodiacetic acid
and a diol or mixture of diols, wherein said diol is an aliphatic diol
containing from 2-6 carbon atoms and primary alcohol functional groups;
a dinitramide salt oxidizer in the range from about 50% to about 70% by
weight of the composite propellant formulation, wherein the dinitramide
salt oxidizer is selected from ammonium dinitramide (ADN), tetrazolium
dinitramide, ammoniumtetrazole dinitramide, aminoammoniumfurazan
dinitramide, and mixtures thereof;
a reactive metal in the range from about 0% to about 25% by weight of the
composite propellant formulation, wherein the reactive metal is selected
from aluminum, magnesium, aluminum-magnesium alloys, boron, and mixtures
thereof; and
a polyfunctional curative.
20. A composite propellant formulation as defined in claim 19, wherein the
diol is selected from 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol,
1,5-pentanediol, 1,6-hexanediol, diethyleneglycol, triethyleneglycol,
tetraethyleneglycol, 2,2-dinitro-1,3-propanediol, and mixtures thereof.
21. A composite propellant formulation as defined in claim 1, wherein the
energetic binder is poly-NMMO (poly(nitratomethyl-methyloxetane)).
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to low-hazard solid rocket propellant formulations
which use little or no chlorine-containing oxidizers. More specifically,
the present invention relates to propellant formulations based on a
dinitramide salt oxidizer and an energetic binder.
2. Technology Background
Solid propellants are used extensively in the aerospace industry and are a
preferred method of powering most missiles and rockets for military,
commercial, and space applications. Solid rocket motor propellants have
become widely accepted because they are relatively simple to manufacture
and use, and because they have excellent performance characteristics.
Typical solid rocket motor propellants are formulated using an oxidizing
agent, a fuel, and a binder. At times, the binder and the fuel may be the
same. In addition to the basic components, it is conventional to add
various bonding agents, plasticizers, curing agents, cure catalysts, and
other similar materials which aid in the processing or curing of the
propellant or contribute to mechanical properties improvements of the
cured propellant. A significant body of technology has developed related
solely to the processing and curing of solid propellants.
Many types of propellants used in the industry use ammonium perchlorate
(AP) as the oxidizer. AP has been a preferred oxidizer because of its high
energy with relatively low associated hazards, its ability to efficiently
oxidize the commonly-used aluminum fuel, and its burn rate tailorability.
However, there is some interest in the industry to identify alternative
oxidizers having similar attractive properties which do not produce
chlorine-containing exhaust products.
A commonly used low-hazard nonchlorine oxidizer is ammonium nitrate (AN).
This oxidizer has also been examined in many types of propellants.
Unfortunately, AN is well known for its poor performance capability, its
inability to combust aluminum efficiently, and the low burn rate of
propellants formulated with only AN as the oxidizer. These problems
continue to plague nonchlorine propellant development efforts.
Accordingly, it would be a significant advancement in the art to provide
propellant formulations of equivalent or improved energy capable
combusting aluminum efficiently, providing high propellant burn rates, and
producing little or no HCl exhaust emissions.
Such propellant formulations are disclosed and claimed herein.
SUMMARY OF THE INVENTION
The invention is directed to the use of a dinitramide salt as the major
oxidizer in combination with an energetic binder in propellant
formulations. Such propellants contain no chlorine when the dinitramide
salt is the only oxidizer or is used in combination with another
nonchlorine oxidizer, or reduced chlorine when the dinitramide salt is
used in combination with AP.
The dinitramide salts used according to the present invention have the
following general formula: X.sup.+ ›N(NO.sub.2).sub.2 !.sup.-, where
X.sup.+ is the cationic counterion. Currently preferred counterions are
those that complement the energetic properties of the dinitramide anion
such as ammonium ion, aminotetrazole ion, urea, biuret, biguanide,
N-heterocyclic-containing basic amines, and diaminofurazan ion. Ammonium
dinitramide (ADN) is a currently preferred oxidizer according to the
present invention.
The propellant formulations of the present invention preferably include an
energetic binder, such as energetically substituted oxetane and oxirane
polymers (any of which may be either plasticized or unplasticized).
Typical energetic substituents include nitromethyl, nitratomethyl,
azidomethyl, and difluoroaminomethyl. Reactive metals, such as aluminum,
magnesium, aluminum-magnesium alloys, and boron, can also be included in
the propellant formulations of the present invention. Propellant
formulations useful for minimum smoke or reduced smoke applications,
preferably include little or no reactive metal.
It has been found that propellant formulations containing a dinitramide
salt, aluminum, and energetic binder possess high burn rates in a range
comparable to propellants containing ammonium perchlorate.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to low-hazard solid rocket propellant
formulations which do not require use of a chlorine-containing oxidizer.
Dinitramide salts are used in combination with energetic binders to
produce composite propellant formulations having high burn rates and
performance comparable to conventional propellants based on ammonium
perchlorate. Importantly, the propellants of the present invention do not
produce high levels of chlorine-containing exhaust products. A method of
forming dinitramide salts is disclosed in U.S. Pat. No. 5,198,204, granted
Mar. 30, 1993, which is incorporated herein by reference.
The dinitramide salts used according to the present invention have the
following general formula: X.sup. +›N(NO.sub.2).sub.2 !.sup.-, where
X.sup.+ is the cationic counterion. Currently preferred counterions are
those that complement the energetic properties of the dinitramide anion
such as ammonium ion (NH.sub.4.sup.+), aminotetrazole ion, having the
following structure:
##STR1##
urea, biuret, biguanide, and diaminofurazan ion having the following
structure:
##STR2##
Cations of nitrogen containing heterocycles having the following general
structure are preferred.
##STR3##
Where X is N, O, or CH.sub.2 ; Y is N, CNH.sub.2, CH, or CNO.sub.2 ; and Z
is H, NH.sub.2, or NHNO.sub.2. Cations based on polycyclic polyamines such
as bitetrazole, azobitetrazole, bitetrazoleamine, azoaminobitetrazole,
analogous triazoles, and the like are also preferred counterions. Other
possible cationic counterions which can be used with dinitramide anions
include 1-8 nitrogen-containing cations of the formula (R".sub.k H.sub.m
N.sub.n).sup.+z, wherein n=1 to 8, k=0 to 2+n, z=1 to n, m=3+n-k, and each
R" is the same or different 1-6 carbon straight chain or branched alkyl.
Examples of such ions include NH.sub.4.sup.+, CH.sub.3 NH.sub.3.sup.+,
(CH.sub.3).sub.2 NH.sub.2.sup.+, (CH.sub.3).sub.3 NH.sup.+,
(CH.sub.3).sub.4 N.sup.+, C.sub.2 H.sub.5 NH.sub.4.sup.+, (C.sub.2
H.sub.5).sub.2 NH.sub.2.sup.+, (C.sub.2 H.sub.5).sub.3 NH.sup.+, (C.sub.2
H.sub.5).sub.4 N.sup.+, (C.sub.2 H.sub.5)(CH.sub.3)NH.sub.2 .sup.+,
(C.sub.2 H.sub.5)(CH.sub.3).sub.2 NH.sup.+, (C.sub.2 H.sub.5).sub.2
(CH.sub.3).sub.2 N.sup.+, (C.sub.3 H.sub.7).sub.4 N.sup.+, (C.sub.4
H.sub.9).sub.4 N.sup.+, N.sub.2 H.sub.5.sup.+, CH.sub.3 N.sub.2
H.sub.4.sup.+, (CH.sub.3).sub.2 N.sub.2 H.sub.3.sup.+, (CH.sub.3).sub.3
N.sub.2 H.sub.2.sup.+, (CH.sub.3).sub.4 N.sub.2 H.sup.+, (CH.sub.3).sub.5
N.sub.2.sup.+, etc. Ammonium dinitramide (ADN) is a currently preferred
oxidizer according to the present invention.
Energetic binders which are used in the propeilant formulations of the
present invention include energetically substituted oxetane, oxirane
polymers, and nitramine polymers (any of which may be either plasticized
or unplasticized). Typical energetic substituents include nitromethyl,
nitratomethyl, azidomethyl, and difluoroaminomethyl. A currently preferred
class of energetically substituted oxetane polymers is represented by the
following formula:
##STR4##
where X is --NO.sub.2, --ONO.sub.2, --N.sub.3, --NF.sub.2, or --H and Y is
--NO.sub.2, --ONO.sub.2, --N.sub.3, or --NF.sub.2. The 3,3-disubstituted
oxetanes are preferred over other substitution, such as the
2,4-disubstituted oxetanes, because they are easier to prepare and less
expensive.
A currently preferred class of energetically substituted oxirane polymers
is represented by the following formula:
##STR5##
where X is --NO.sub.2 or --N.sub.3. Poly(glycidyl nitrate) and
poly(glycidyl azide) are two currently preferred oxirane polymers.
A currently preferred class of nitramine polymers are polyesters based on
nitraminodiacetic acid and a diol or mixture of diols. Suitable diols are
aliphatic diols containing from 2-6 carbon atoms and primary alcohol
functional groups. The diol can contain ether linkages, but the diol
molecule preferably does not also contain an ester or ketone. Examples of
suitable diols include 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol,
1,5-pentanediol, 1,6-hexanediol, diethyleneglycol, triethyleneglycol,
tetraethyleneglycol, and 2,2-dinitro-1,3-propanediol.
Specific energetic binders useful in the present invention include PGN
(poly(glycidyl nitrate)), poly-NMMO (poly(nitratomethyl-methyloxetane)),
GAP (glycidyl azide polymer), 9DT-NIDA
(diethyleneglycoltriethyleneglycol-nitraminodiacetic acid terpolymer),
poly-BAMO (poly(bisazido-methyloxetane)), poly-AMMO
(poly(azidomethyl-methyloxetane)), poly-NAMMO
(poly(nitraminomethyl-methyloxetane)), copoly-BAMO/NMMO, copoly-BAMO/AMMO,
and mixtures thereof.
Reactive metals, such as aluminum, magnesium, aluminum-magnesium alloys,
and boron, are optionally included in the the performance requirements of
the propellant formulation. For those propellant formulations designed to
produce little or no smoke, little or no reactive metal is used.
A typical solid propellant formulation within the scope of the present
invention has the following ingredients:
______________________________________
Ingredient Weight %
______________________________________
Energetic binder 10-35
Reactive metal 0-25
Dinitramide salt 50-70
Curatives/stabilizers
2-5
______________________________________
The lower range of reactive metal (about 0% to 5%, preferably 1% to 5%)
includes "reduced smoke" formulations, while the upper limit (25%) covers
typical composite propellant formulations. Solids loadings in the range
from about 65% to 90%, by weight, are typical. Solids loadings from 70% to
80%, by weight, according to the present invention, provide energy
comparable to conventional composite propellant formulations at 88-90%
solids containing an inert binder such as HTPB and AP oxidizer. The lower
oxidizer loadings contribute to reduced hazards, and the lower reactive
metal loadings contribute to reduced exhaust particulates.
The following examples are offered to further illustrate the present
invention. These examples are intended to be purely exemplary and should
not be viewed as a limitation on any claimed embodiment.
EXAMPLE 1
A composite propellant formulation having 72% solids was prepared having
the following ingredients:
______________________________________
Ingredient Weight %
______________________________________
PGN 24.4
Al (30 .mu.m) 13
ADN 59
Curatives/Stabilizers
3.6
______________________________________
The curatives and stabilizers included 0.4% NO.sub.x scavenger MNA
(N-methyl-p-nitroaniline), 3.11% Desmodur.RTM. N-100, a polyisocyanate
curative obtained from Mobay, 0.05% acid scavenger
(N,N,N',N'-tetramethyl-1,8-naphthalenediamine, obtained from Aldrich), and
0.005% cure catalyst TPB (triphenyl bismuth).
The PGN (poly(glycidyl nitrate)), MNA, and acid scavenger were added to a
warm mixer bowl (120.degree. F.) and mixed at slow speed for 10 minutes.
The aluminum was added and mixed at slow speed for 5 minutes. The ADN was
added in one third increments over 30 minutes. All ingredients were then
mixed for an additional 10 minutes under vacuum. Finally, the isocyanate
curative and TPB were added and mixed at low speed for 10 minutes under
vacuum. The propellant was cast and cured at 120.degree. F. for 6 days.
The composite propellant had a burn rate at 1000 psi of 0.76 ips. By way of
comparison, the burn rate of similar propellant formulations containing AN
as the oxidizer have burn rates of about 0.2 ips at 1000 psi. The
composite propellant had a pressure exponent from 500 to 1800 psi of 0.67
with a slope break observed near 2000 psi. Optical bomb tests show
desirable ease of ignition and efficient aluminum combustion
characteristics, comparable to AP and much better than other nonchlorine
oxidizers such as AN. The thermo-chemically predicted performance of the
ADN formulation is significantly better than either the AN or AP oxidized
analogous formulations, according to the calculations summarized in Table
1, below.
Safety tests of this composite propellant indicate no ESD (electrostatic
discharge) sensitivity due to the polar binder. Impact sensitivity was
typical of a Class 1.3 composite (nondetonable) propellant, while friction
sensitivity was slightly greater than a typical Class 1.3 composite
propellant.
EXAMPLE 2
A composite propellant formulation having 72% solids is prepared according
to Example 1, except that 5% aluminum and 67% ADN, by weight are included.
It is expected that this propellant formulation has a slightly slower burn
rate with cooler flame temperature than the propellant of Example 1.
Significantly, the energy of this reduced smoke propellant is similar to
metallized (16% Al) composite/AP propellant formulations, as summarized in
Table 1, below.
EXAMPLE 3
A composite propellant formulation having 72% solids is prepared according
to Example 1, except that 18% aluminum and 54% ADN, by weight are
included. It is expected that this propellant formulation has additional
performance enhancement with a possibly reduced pressure exponent than the
propellant of Example 1, as summarized in Table 1, below.
EXAMPLE 4
A composite propellant formulation having 72% solids is prepared according
to Example 1, except that 14.75% ammonium perchlorate (200 .mu.m), by
weight, replaces a like amount of the ammonium dinitramide. It is
thermochemically predicted that this propellant formulation would contain
about 4.5% HCl in its exhaust which is a significant reduction over
standard AP propellant formulations. Processing may be improved, compared
to the propellant formulation of Example 1. The presence of AP in the
formulation adds another variable for ballistic control.
EXAMPLE 5
A composite propellant formulation having 72% solids is prepared according
to Example 1, except that 20% ammonium nitrate (200 .mu.m), by weight,
replaces a like amount of the ammonium dinitramide. It is expected that
this nonchlorine propellant formulation may have a reduced burn rate,
compared to the propellant formulation of Example 1, as summarized in
Table 1, below. However, it is also expected that this formulation will
have lower cost and likely reduced hazards sensitivity, while maintaining
very good performance.
Theoretical performance calculations using the NASA-Lewis thermochemical
code were performed on the propellant compositions of Examples 1-5 which
are summarized below in Table 1:
TABLE 1
______________________________________
Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5
______________________________________
Ingredient
Al 13.00 5.00 18.00 13.00 13.00
AP
0-
0-
0- 14.75
0-
AN
0-
0-
0-
0- 20.00
ADN 59.00 67.00 54.00 44.25 39.00
Binder/ 28.00 28.00 28.00 28.00 28.00
curative
Property
Density 0.0628 0.0612 0.0638 0.0635 0.0622
lb/in.sup.3
.DELTA.Isp,
+8.24 +4.17 +9.15 +5.70 +3.06
sec.dagger.
.DELTA.Isp .multidot.
+0.14 -0.58 +0.50 +0.19 -0.35
Density
Flame 3263 2997 3410 3272 3100
Temp., .degree.C.
% HCl,
0-
0-
0- 4.49
0-
Exhaust
______________________________________
.dagger.As compared to a production composite AP propellant formulation
(16% Al).
From the data depicted in Table 1, it can be appreciated that ADN may
either fully or partially replace AP as an oxidizer in propellant
formulations without greatly sacrificing propellant performance, even at
reduced metal loadings (13% Al versus the 16% Al comparison propellant).
There is some reduction in propellant density, but a significant increase
in Isp offsets this reduction. Importantly, the quantity of HCl in the
propellant exhaust products can be eliminated or substantially reduced. In
the reduced smoke formulation, Example 2, 5% Al expectedly gives lower
performance than the highly metallized formulations, but the energy for
this class of propellants is very good.
EXAMPLE 6
Theoretical performance calculations using the NASA-Lewis thermochemical
code were performed on propellant compositions containing 13% Al, 59%
oxidizer (either ADN, AP, or AN), and 28% PGN binder/curative.
TABLE 2
______________________________________
Theoretical Performance Comparison of ADN, AP,
and AN in PGN-based Propellant
Oxidizer
ADN AP AN
______________________________________
Ingredient
Al 13.00 13.00 13.00
AP
0- 59.00
0-
AN
0-
0- 59.00
ADN 59.00
0-
0-
Binder/curative
28.00 28.00 28.00
Property
Density, lb/cu. in.
0.06276 0.06563 0.06124
Isp, sec. 293.53 282.97 276.05
(Density).sup.0.75 (Isp)
36.81 36.69 33.98
Flame Temperature, .degree.C.
3263 3291 2733
Measured Burn 0.76 0.3-0.4 0.2-0.3
rate @ 1000 psi, ips
______________________________________
Isp = Isp(vac) at P.sub.c = 1000 psi, Expansion Ratio (A.sub.c /A.sub.t)
10 (A.sub.c = area of exit and A.sub.t = area of throat).
(Density).sup.0.75 (Isp) is a common performance/volume efficiency
comparison.
From the results reported in Table 2, the energy-density for the ADN
composition is superior to the AP-analogue; the lower density of ADN is
offset by its extremely high Isp. Although hydrocarbon binders, such as
HTPB or PBAN are most commonly used and represent the obvious choice, they
are not selected herein because of binder compatibility problems discussed
below.
ADN propellant compositions containing an energetic binder provide a
significant advantage over known non-chlorine propellant compositions
because the high energy-density can be obtained at lower oxidizer loadings
and lower Al loadings. The lower oxidizer loadings contribute to reduced
hazards, and the lower Al loadings contribute to reduced exhaust
particulates.
EXAMPLE 7
Propellant compositions containing the combination of ADN and PGN produce
energy competitive with current high solids, AP-oxidized propellants, as
reported in Table 3.
TABLE 3
______________________________________
ADN Propellant Comparison with
Commercial Class 1.3 Composite Propellants
Binder PGN HTPB.sup.a
PBAN.sup.b
______________________________________
Oxidizer (wt. %)
59% ADN 68.9% AP 70% AP
Fuel (wt. %) 13% Al 19% Al 16% Al
Total Solids 72% 88% 86%
Density, lb/cu. in.
0.06276 0.06518 0.06408
Isp, sec* 293.53 287.23 285.29
(Density).sup.0.75 (Isp)
36.81 37.05 36.34
Flame Temp., .degree.C.
3262 3290 3154
Al.sub.2 O.sub.3 (exit),
0.25 0.35 0.30
mass fraction
______________________________________
*Isp = Isp(vac) at P.sub.c = 1000 psi, A.sub.c /A.sub.t = 10.
.sup.a Castor 120 .RTM. propellant formulation, including Fe.sub.2 O.sub.
catalyst.
.sup.b Space shuttle propellant formulation, excluding Fe.sub.2 O.sub.3
catalyst.
EXAMPLE 8
A composite propellant formulation having 72% solids is prepared according
to Example 1, except that ammoniumtetrazole (ATDN) replaces the ammonium
dinitramide. It is expected that this nonchlorine propellant formulation
may have slightly reduced energy, compared to the propellant formulation
of Example 1. However, it is also expected that this formulation will have
a lower flame temperature, while maintaining very good performance.
EXAMPLE 9
A composite propellant formulation having 72% solids is prepared according
to Example 1, except that aminoammoniumfurazan (DAFDN) replaces the
ammonium dinitramide. It is expected that this nonchlorine propellant
formulation may have slightly reduced energy, compared to the propellant
formulation of Example 1. However, it is also expected that this
formulation will have a lower flame temperature, while maintaining very
good performance.
Theoretical performance calculations in which the oxidizer dinitramide
counter ion is ammoniumtetrazole (ATDN) or the aminoammoniumfurazan
(DAFDN) (Examples 8 and 9) are shown below in Table 4:
TABLE 4
______________________________________
Ex. 8 Ex. 9
______________________________________
Ingredient
Al 13.00 13.00
ATDN 59.00
0-
DAFDN
0- 59.00
Binder/curative 28.00 28.00
Property
Density lb/in.sup.3
0.0626 0.0624
.DELTA.Isp, sec.dagger.
-2.01 -0.01
.DELTA.Isp .multidot. Density
-0.56 -0.49
Flame Temp., .degree.C.
3017 2972
% HCl, Exhaust
0-
0-
______________________________________
.dagger.As compared to a production composite AP propellant formulation
(16% Al).
While slightly lower in energy than the analogous ADN formulation (Example
1 of Table 1), the formulations depicted in Table 4 can be useful in
systems requiring a cooler flame temperature or a lower oxygen/fuel ratio
for exhaust species modification. Because these ATDN and DAFDN oxidizers
have a lower oxygen content, they would also be useful in reduced smoke
(0%-5% metal) formulations.
EXAMPLE 10
Theoretical performance calculations using the NASA-Lewis thermochemical
code were performed on propellant compositions containing 13% Al, 59% ADN
and a variety of different energetic binders within the scope of the
present invention. The results of these calculations are reported below in
Table 5. The PGN formulation of Example 1 is included for comparison.
TABLE 5
__________________________________________________________________________
Binder polymer/
NMMO/
BAMO--AMMO/
GAP/ 9DT--
plasticizer
NMMO BuNENA
GAP--P GAP--P
NIDA PGN
__________________________________________________________________________
Pl/Po -- 1.0 2.0 2.0 -- --
Density, lb/in.sup.3
0.06021
0.05979
0.05995 0.06022
0.06134
0.06276
Isp, sec*
292.77
295.50
295.96 295.24
286.19
293.53
Density.sup.(0.75) .multidot. Isp
35.59 35.73
35.86 35.89 35.27 36.81
Flame Temp., .degree.C.
3034 3084 3062 3086 3026 3262
__________________________________________________________________________
*Isp = Isp(vac) at P.sub.c = 1000 psi, A.sub.c /A.sub.t = 10.
The energetic plasticizer BuNENA is butyl nitratoethyl-nitramine and GAP-P
is GAP plasticizer. GAP plasticizer has the same polymer backbone as GAP,
but is terminated with non-reactive end groups instead of hydroxyl groups.
These formulations illustrate the utility of the energetic oxetanes,
oxiranes, and nitramine polymers. The Isp values show the performance
improvement potential over typical Class 1.3 composite propellants like 86
percent solids, 16 percent aluminum PBAN propellant (Isp=285.29) or 88
percent solids, 19 percent aluminum HTPB propellant (Isp=287.23). These
performance numbers are particularly impressive because the ADN
formulations are relatively low solids, low metal, and totally
non-chlorine.
Although the propellant formulations shown above are all at 72 weight
percent solids and 13% aluminum to facilitate comparison with the
previously reported PGN propellant formulation, the propellant
formulations have not been optimized for performance. It is likely each
system will be optimized for overall performance at slightly different
ingredient weight percents. The optimum performance will likely be
improved slightly compared to the numbers reported above.
From the foregoing it will be appreciated that the present invention
provides propellant formulations exhibiting efficient aluminum combustion
and high propellant burn rates, while producing reduced or no
chlorine-containing exhaust products. The propellant formulations also
provide excellent performance in reduced smoke applications.
The invention may be embodied in other specific forms without departing
from its essential characteristics. The described embodiments are to be
considered in all respects only as illustrative and not restrictive. The
scope of the invention is, therefore, indicated by the appended claims
rather than by the foregoing description. All changes which come within
the meaning and range of equivalency of the claims are to be embraced
within their scope.
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